Since photographic light-sensitive materials are generally composed of an electrically insulating support base (hereinafter also more simply referred to as the support) and photographic emulsion layers, it is frequently observed that friction therebetween or with other substances or peeling of the light-sensitive materials during the production or upon use induces accumulation of static charge. The accumulated static charge causes various problems, one of, and the most serious of which, is that the static electricity accumulated before development processing is discharged so as to expose the light-sensitive emulsion layers to light. When the light-exposed photographic film is subjected to development processing, dots or arborescent or feathery lines that are called static marks are formed on the photographic films, thus significantly impairing or sometimes completely destroying the commercial value of the film. For example, appearance of the static marks on X-ray films for medical or industrial use may lead to incorrect and dangerous judgment. This phenomenon, i.e., formation of static marks, is a very difficult problem, because it does not evidence itself until the film is developed. Accumulated static charge also causes other problems, such as adhesion of dust on film surfaces and difficulty in uniform coating.
Such static charge is easily accumulated during the production or use of photographic light-sensitive materials as described above. For example, static electrification results from (1) contact friction between a photographic film and rollers; (2) separation between a support surface and an emulsion surface during winding or re-winding of the film roll in the course of production; (3) separation between a base surface and an emulsion surface during winding of the final photographic film product; (4) contact and separation between the film and machinery parts or fluorescent-sensitized paper in an automatic photographic machine for X-ray films. Contact with wrapping materials also causes static electrification. The static marks on the photographic light-sensitive materials induced by the above-described accumulation of static charge become even more significant with an increase in the sensitivity of the photographic light-sensitive material or an increase of processing rates. In particular, recent developments improving the sensitivity of photographic light-sensitive materials and the speeds of coating, photographing, and automatic development processing and the like have subjected such light-sensitive materials to severe conditions, tending to result in more frequent occurrence of static marks.
A commercial product of X-ray films generally contains a number of X-ray films with papers inserted between the films so as not to contact individual films with each other. When the X-ray films are stored for a long period of time while contacting the paper, static marks are liable to occur on the film due to the decrease in static property of light-sensitive materials, even though the films just after production have sufficient antistatic property. Although the reason for decreasing the antistatic property with the passage of time has not been completely understood, it is highly probable that a certain type of nonionic surface active agents present on the surface of the light-sensitive materials is diffused or transferred to the paper during the storage. Thus, it is highly desirable to develop light-sensitive materials which substantially do not decrease their antistatic property during the storage while contacting with papers.
In order to eliminate these disturbances ascribed to static electricity, it is preferable to add an antistatic agent to the photographic light-sensitive materials. However, antistatic agents commonly employed in other fields cannot be applied as such to photographic light-sensitive materials because of various limitations inherent to photographic light-sensitive materials. In other words, antistatic agents employable for photographic light-sensitive materials are required to have various specific performances, such as that: they are required not only to exhibit an excellent antistatic property but also to have no adverse influence on photographic properties of the photographic light-sensitive materials such as sensitivity, fog, graininess, sharpness, etc., to have no adverse influence on film strength of the light-sensitive materials (i.e., not to make the film surface more susceptible to damages due to friction or scratches), to have no adverse influence on adhesion resistance of the light-sensitive materials (i.e., not to make the film surfaces stick to each other or to other substances), not to accelerate fatigue of processing solutions, not to contaminate carrying rollers, not to reduce an adhesive strength between layers constituting the photographic light-sensitive materials, and so on.
Another method for overcoming the above-described problems due to static electricity comprises increasing electric conductivity of the surface of the photographic light-sensitive materials, thereby dispersing the static electricity in a short period of time before the accumulated electric charge discharges with adverse effects.
For this purpose, many methods for increasing conductivity of the support base or various coating layers have been developed, and use of a variety of hydroscopic substances or water-soluble organic salts, certain kind of surface active agents or polymers, etc., have been attempted.
Of these, use of surface active agents is important for prevention of static electricity. Known surface active agents include, for example, anionic, betaine and cationic surface active agents described in U.S. Pat. Nos. 3,082,123, 3,201,151, 3,519,561 and 3,625,695, West German Patent Nos. 1,552,408 and 1,597,472, Japanese Patent Application (OPI) (Open to Public Inspection) Nos. 85826/74, 129623/78, 159223/79 and 19213/73 and Japanse Patent Publication Nos. 39312/71, 11567/74, 46755/76 and 14417/80, etc.
These known surface active agents, however, show specificity depending on the kind of the film supports or photographic compositions. For example, they afford good results to some specific film supports, photographic emulsion layers or other photographic layers, but are not at all effective on other film supports or photographic layers; or, although their antistatic property is excellent, they may adversely affect photographic properties, e.g., sensitivity, fog, graininess, sharpness, etc., or cause contamination of developing solutions and adhesion on rollers. Thus, it has been quite difficult to successfully apply such known substances to photographic light-sensitive materials.
Further, techniques for static charge prevention by the use of nonionic surface active agents are closely related to coating agents with which they are used in combination. Although some progress is certainly being made toward achieving the antistatic property per se, no consideration has been given to the prevention of contamination of developing solutions or carrying rollers, which can lead to serious disorders of photographic films.
For instance, Japanese Patent Publication No. 9610/76 is disclosed that an ethylene oxide-added polymer of a phenol-formalin condensate is excellent in antistatic property even when used in combination with various coating agents. However, this method still cannot overcome the problem due to contamination during development processing. In other words, according to this method, contamination of carrying rollers, which is believed to arise from dry attachment on the rollers, is significant, and gives rise to the problem of uneven film concentration.
Furthermore, Japanese Patent Application (OPI) No. 29715/78 describes a photographic light-sensitive material containing a specific anionic surface active agent and a polyoxyethylene-based nonionic surface active agent, but such a light-sensitive material cannot achieve elimination of film disorders due to contamination of developing solutions or carrying rollers such as were noted above.
Many of these conventional techniques for providing photographic light-sensitive materials with antistatic property result in good antistatic effect just after preparation of the light-sensitive materials, but the antistatic effect tends to decrease with the passage of time. For this reason, technique for providing long-lasting antistatic effect has long been demanded.